Nitrogen Fixation Efficiency Research Articles

Differential responses of Bradyrhizobium sp. SUTN9-2 to plant extracts and implications for endophytic interactions within different host plants

Bradyrhizobium sp. strain SUTN9-2 demonstrates cell enlargement, increased DNA content, and efficient nitrogen fixation in response to rice (Oryza sativa) extract. This response is attributed to the interaction between the plant’s cationic antimicrobial peptides (CAMPs) and the Bradyrhizobium BacA-like transporter (BclA), similar to bacteroid in legume nodules. The present study reveals that SUTN9-2 can also establish functional endophytic interactions with chili (Capsicum annuum) and tomato (Solanum lycopersicum) plants. When exposed to extracts from chili and tomato, SUTN9-2 exhibits cell elongation, polyploidy, and reduced cell viability, with the effects being less pronounced for tomato extract. Transcriptomic and cytological analyses revealed that genes associated with CAMP resistance, nitrogen metabolism, nitrogen fixation, defense responses, and secretion systems were upregulated, while genes related to the cell cycle and certain CAMP-resistance mechanisms were downregulated, particularly in response to chili extract. This study suggests that SUTN9-2 likely evolves resistance mechanisms against CAMPs found in rice, chili, and tomato plants through mechanisms involving the protease-chaperone DegP, AcrAB-TolC multidrug efflux pumps, and polysaccharides. These mechanisms facilitate efflux, degradation, and the formation of protective barriers to resist CAMPs. Such adaptations enable SUTN9-2 to persist and colonize host plants despite antimicrobial pressures, influencing its viability, cell differentiation, and nitrogen fixation during endophytic interactions with various plant hosts.

Reshape Iron Nanoparticles Using a Zinc Oxide Nanowire Array for High Efficiency and Stable Electrocatalytic Nitrogen Fixation.

As a type of century-old catalyst, the use of iron-based materials runs through the Haber-Bosch process and electrochemical synthesis of ammonia because of its excellent capability, low cost, and abundant reserves. How to continuously improve its catalytic activity and stability for electrochemical nitrogen fixation has always been a goal pursued by scientific researchers. Herein, we develop a free-standing iron-based catalyst, i.e., the iron nanoparticles with zinc oxide nanowire array support (Fe/ZnO NA), which exhibits a high ammonia yield of ∼54.81 μg h-1 mgcat.-1 and a Faradaic efficiency (FE) of ∼9.56% in a 0.5 M potassium hydroxide solution, along with good reusability and durability. Its electrocatalytic ability is superior to that of commercial Fe materials and most reported Fe-based catalysts, thus showing great competitiveness. This is because the ZnO NA not only supplies stable support for the homogeneous dispersion of Fe nanoparticles but also provides a very beneficial synergy to their catalytic activity. The work renews traditional iron-based catalysts and is thus of great significance for promoting the industrialization of electrochemical ammonia synthesis.

Highly efficient photocatalytic nitrogen fixation of ZnWO4/g-C3N4 S-scheme heterojunction nanofibers: Synergistic effect of water molecules deprotonation and photogenerated electrons

Highly efficient photocatalytic nitrogen fixation of ZnWO4/g-C3N4 S-scheme heterojunction nanofibers: Synergistic effect of water molecules deprotonation and photogenerated electrons

Mixed-metal MIL-101(Fe/Cr) MOF photocatalyst: Efficient photocatalytic nitrogen fixation by promoting ligand-metal charge transfer

Mixed-metal MIL-101(Fe/Cr) MOF photocatalyst: Efficient photocatalytic nitrogen fixation by promoting ligand-metal charge transfer

Single-Atom Mo Supported by TiO2 for Photocatalytic Nitrogen Fixation.

The challenge of achieving efficient photocatalysts for the fixation of ambient nitrogen to ammonia persists. The utilization efficiency of single-metal-atom catalysts leads to an increased number of active sites, while their distinctive geometrical and electronic characteristics contribute to enhancing the intrinsic activity of each individual site. In this study, we present a method using an organic molecule to assist in loading TiO2 with Mo single atoms for the purpose of photocatalytic nitrogen fixation. By adjusting the number of Mo single atoms loaded, we were able to regulate the microenvironment surrounding the catalytic center. Our results demonstrate that TiO2-Mo10 achieved a remarkable photocatalytic nitrogen fixation performance of 42.05 μmol·g-1·h-1 at room temperature while maintaining excellent structural stability and cycle life. The incorporation of Mo single atoms effectively enhanced electron separation and migration within TiO2, leading to a significant weakening of the N≡N bond. This research highlights the potential for predesigning TiO2-based single-atom photocatalysts with tailored structures for efficient nitrogen fixation through photocatalysis. These findings offer valuable insights for the future development and rational design of single-atom photocatalysts.

Enacting partner specificity in legume–rhizobia symbioses

AbstractLegumes, such as peas, beans, and alfalfa, have evolved a remarkable ability to establish root nodule symbioses with nitrogen-fixing soil bacteria to fulfill their nitrogen needs. This partnership is characterized by a high degree of specificity, occurring both within and between host and bacterial species. Consequently, nodulation capacity and nitrogen-fixing efficiency vary significantly among different plant–bacteria pairs. The genetic and molecular mechanisms regulating symbiotic specificity are diverse, involving a wide array of host and bacterial genes and signals with various modes of action. Understanding the genetic basis of symbiotic specificity could enable the development of strategies to enhance nodulation capacity and nitrogen fixation efficiency. This knowledge will also help overcome the host range barrier, which is a critical step toward extending root nodule symbiosis to non-leguminous plants. In this review, we provide an update on our current understanding of the genetics and evolution of recognition specificity in root nodule symbioses, providing more comprehensive insights into the molecular signaling in plant–bacterial interactions.

Quantification of Indigenous Rhizobial Populations Associated with Pea Nodulation in Kumaon Region of North-western Himalayas

The purpose of this study was to explore the diversity of native rhizobial populations in pea-cultivating regions of the Kumaon area in the north-western Himalayas and their role in biological nitrogen fixation (BNF). The research employed completely randomized design (CRD), involving the collection of soil samples from 12 locations to analyze rhizobial populations, soil physicochemical properties, and their effects on pea nodulation and nitrogen accumulation. A positive correlation was observed between soil organic carbon (OC) levels and the most probable number (MPN) of rhizobia, with higher OC supporting greater rhizobial growth and BNF. Sites such as Daranti and Khamaria, with elevated OC levels, exhibited higher rhizobial populations and enhanced nodulation, while regions with lower OC, such as Chafi and Sui, showed reduced activity. Daranti recorded the highest rhizobial count 10,000 g⁻¹ of soil, and Timiladiggi demonstrated superior nitrogen fixation efficiency (18.01 mg plant⁻¹ BNF). These findings suggest the potential for isolating and using efficient rhizobial strains, such as those from Timiladiggi, as inoculants to improve BNF in less fertile areas. The study also identified climatic influences on soil properties, with cooler, high-altitude regions promoting greater OC accumulation and rhizobial activity. These results emphasize the importance of utilizing efficient rhizobial strains and enhancing soil OC to boost legume productivity and support sustainable agriculture in diverse agroclimatic zones. Future research should focus on metagenomic analyses to characterize the genetic diversity of native rhizobia and uncover their functional traits.

Increased diversity of beneficial rhizobia enhances faba bean growth

Legume-rhizobium symbiosis provides a sustainable nitrogen source for agriculture. Nitrogen fixation efficiency depends on both legume and rhizobium genotypes, but the implications of their interactions for plant performance in environments with many competing rhizobium strains remain unclear. Here, we let 399 Rhizobium leguminosarum complex sv. viciae strains compete for nodulation of 212 faba bean genotypes. We find that the strains can be categorised by their nodule occupancy profiles into groups that show distinct competitive interactions and plant growth-promoting effects. Further, we show that the diversity of strains occupying root nodules affects plant growth and is under plant genetic control. These insights provide a basis for re-designing rhizobium inoculation and plant breeding strategies to enhance symbiotic nitrogen fixation in agriculture.

Hybrid Soybean as Green Manure for Improving Soil Properties and Subsequent Crop Growth

The rapid increase in fertilizer use has led to the degradation of soil quality, nutrient imbalances, reduced biodiversity, and soil compaction. To address these challenges, hybrid soybeans with efficient biological nitrogen fixation capabilities and broad environmental adaptability were selected as green manure to reduce fertilizer application, thereby improving soil fertility and structure. This study utilized the varieties “Forage Soybean S001” (S001), “Neinong S002 Forage Soybean” (S002), “Mengnong S003 Forage Soybean” (S003), “Mengnong S004 Forage Soybean” (S004), “Mengnong S005 Forage Soybean” (S005), and “Mengnong S006 Forage Soybean” (S006) as green manure materials. The clean tillage (CK) treatment served as the control, ensuring a residue-free soil surface while maintaining consistent practices in soil preparation, irrigation, and field management across all treatments. Field planting of green manure and subsequent crops was conducted at the M-Grass Ecology and Environment (Group) Company’s experimental site in Hohhot in early May of 2023 and 2024. The plots each measured 20 m2, with three replications arranged in a randomized block design. A combination of field experiments and laboratory analyses was utilized to investigate the effects of incorporating various hybrid soybean varieties as green manure on soil nutrient levels, soil enzyme activity, soil microbial communities, and the subsequent growth of oats. The results indicated that incorporating various hybrid soybean varieties as green manure into the soil significantly improved soil nutrient levels and enzyme activity. The diversity and richness of soil bacterial communities increased significantly, accompanied by alterations in community structure and composition. These changes enhanced soil fertility and optimized the microbial community structure, promoting the growth of subsequent crops. Among all the treatments, S001 and S004 were particularly effective in enhancing the soil environment, indicating their potential as superior green manure resources for broader application.

Cooperation-doping cobalt and boron on MOF with double cone microrods structure to boost efficient nitrogen fixation in Zn-N2 batteries

Cooperation-doping cobalt and boron on MOF with double cone microrods structure to boost efficient nitrogen fixation in Zn-N2 batteries

Construction of dual Z-scheme heterostructure TCN/In2O3/ZnO composite with oxygen vacancies for enhanced artificial nitrogen fixation

The synergistic effect between vacancy engineering and heterostructures can effectively improve the interfacial charge transfer ability and efficiency of catalytic nitrogen reduction. Herein, a ternary dual Z-scheme tubular carbon nitride composited oxygen vacancy-induced indium oxide and oxygen vacancy-induced zinc oxide catalyst (TCN/Vo-In2O3/Vo-ZnO) was constructed, and the synergistic mechanism of charge transport at the catalyst interface was explored. The excellent efficiency of nitrogen fixation could reach 171.56 μmol/L within 120 min, and the high stability of TCN/Vo-In2O3/Vo-ZnO was favorable for practical applications. All experiments indicated that the dual-Z scheme heterostructure and oxygen vacancies have a synergistic effect. Oxygen vacancies could control the valence band position. This control improved the transfer rate of photogenerated charge carriers between heterojunctions, thereby enhancing the adsorption and activation of N2. This study may offer new insights into the synthesis of highly efficient catalysts for photocatalytic nitrogen fixation.

Bacillus velezensis S141 improves the root growth of soybean under drought conditions.

Bacillus velezensis S141 helps soybean establish specific symbiosis with strains of Bradyrhizobium diazoefficiens to form larger nodules and improve nitrogen fixation efficiency. In this study, we found that the dry weight of soybean roots increased significantly in the presence of S141 alone under drought conditions. Hence, S141 improved the root growth of soybean under limited water supply conditions. S141 can produce some auxin, which might be involved in the improved nodulation. Inactivating IPyAD of S141, which is required for auxin biosynthesis, did not alter the beneficial effects of S141, suggesting that the root growth was independent of auxin produced by S141. Under drought conditions, soybean exhibited some responses to resist osmotic and oxidative stresses; however, S141 was relevant to none of these responses. Although the mechanism remains unclear, S141 might produce some substances that stimulate the root growth of soybean under drought conditions.

Responses of Legumes to Rhizobia and Arbuscular Mycorrhizal Fungi Under Abiotic Stresses: A Global Meta-Analysis

Arbuscular mycorrhizal fungi (AMF) and rhizobia play a pivotal role in enhancing crop productivity, shaping microbial community structure, and improving soil quality, making them key components for sustainable ecosystem development. The symbiotic relationship between AMF and rhizobia is crucial for facilitating efficient biological nitrogen fixation and nutrient absorption, thereby reducing the dependence on chemical fertilizers and promoting sustainable agricultural practices. The findings of various studies, however, indicate that soil environment can impede the symbiotic relationship between AMF and rhizobia. We conducted a comprehensive meta-analysis of 158 articles from 1980 to 2022 to explore the synergistic interactions in legume–AMF–rhizobium systems and the potential mechanisms underlying this synergism. Our findings revealed that the inoculation with AMF and/or rhizobia significantly (p < 0.001) increased legume plant nitrogen content, phosphorus content, shoot biomass, yield, AMF colonization rate, and the number and weight of nodules compared to uninoculated controls (effect size d > 0). Moreover, there was a substantial synergistic effect between AMF and rhizobia (p < 0.001). Nevertheless, soil salinity stress, drought stress, and pH stress could hinder the positive effects of inoculation treatments, possibly due to the plant trade-off strategies under abiotic stress conditions. This research may potentially lead to new solutions for sustainable agricultural systems amidst the challenges posed by global climate change.

A Newly Predicted Magnetic TMB6 Monolayer for Efficient Nitrogen Fixation.

Developing electrocatalysts for the N2 reduction reaction (NRR) with high activity, high selectivity, and low cost is urgently required to enhance the NH3 yield rate. Based on first-principles calculations, we predict a series of new transition metal boride TMB6 (TM = Ti, V, Cr, Mn, Fe, and Co) monolayers and investigate their magnetoelectronic and electrocatalytic properties. The results reveal that VB6 and CoB6 favor ferromagnetic coupling, while TiB6, CrB6, MnB6, and FeB6 display antiferromagnetic ordering. Furthermore, TiB6 exhibits a high Néel temperature of 344 K and a large magnetic anisotropy energy of 614 μeV per Ti atom. Most interestingly, TiB6 and VB6 exhibit superior NRR catalytic activity with a limiting potential of -0.50 and -0.19 V, respectively, and favorable NRR selectivity over the HER. Finally, the structural stability of TMB6 monolayers has been confirmed by a set of phonon dispersion, molecular dynamics, and elastic constant calculations. Our results highlight the use of the newly designed two-dimensional (2D) TM borides as promising candidates for spintronic devices and nitrogen fixation applications.

The first principles study of the dual-atom catalyst based on g-C3N5 for efficient nitrogen fixation

Electrocatalytic nitrogen reduction reaction (NRR) for ammonia production has broad prospects because of its mild green reaction conditions. However, the available catalysts cannot meet the needs of industrial ammonia production due to low catalytic activity and poor selectivity. In our work, the dual-atom catalysts (DAC) supported by g-C3N5 with transition metals dual-atom were designed based on the first principles calculation. Based on the criteria of stability, catalytic activity, and the competitive landscape between NRR and hydrogen evolution reaction (HER), the Ni2/g-C3N5 stands out as the most promising candidate among 30 designed diatomic catalysts for NRR, exhibiting remarkable potential for this reaction. In fact, the Ni2/g-C3N5 possesses low limiting potential (−0.27 V) and its selectivity of NRR is nearly 100 %. Importantly, by comprehensively considering the pivotal parameters of charge order, electronegativity, and d-band center, a dedicated descriptive descriptor has been formulated. This result not only profoundly uncovers the intrinsic origins of catalytic activity in the NRR but also significantly expedites the screening process for highly efficient catalysts. Our work not only accelerates the search for an NRR catalyst with high activity but also provides theoretical guidance for subsequent experiments on DACs.

Understanding the Crucial Role of Phosphate and Iron Availability in Regulating Root Nodule Symbiosis.

The symbiosis between legumes and nitrogen-fixing bacteria (rhizobia) is instrumental in sustaining the nitrogen cycle and providing fixed nitrogen to the food chain. Both partners must maintain an efficient nutrient exchange to ensure a successful symbiosis. This mini-review highlights the intricate phosphate and iron uptake and homeostasis processes taking place in legumes during their interactions with rhizobia. The coordination of transport and homeostasis of these nutrients in host plants and rhizobia ensures an efficient nitrogen fixation process and nutrient use. We discuss the genetic machinery controlling the uptake and homeostasis of these nutrients in the absence of rhizobia and under symbiotic conditions with this soil bacterium. We also highlight the genetic impact of the availability of phosphate and iron to coordinate the activation of the genetic programs that allow legumes to engage in symbiosis with rhizobia. Finally, we discuss how the transcription factor phosphate starvation response might be a crucial genetic element to integrate the plant's needs of nitrogen, iron and phosphate while interacting with rhizobia. Understanding the coordination of the iron and phosphate uptake and homeostasis can lead us to better harness the ecological benefits of the legume-rhizobia symbiosis, even under adverse environmental conditions.

Nanoporous Heterojunction Photocatalysts with Engineered Interfacial Sites for Efficient Photocatalytic Nitrogen Fixation.

Photocatalytic N2 reduction reaction (PNRR) offers a promising strategy for sustainable production of ammonia (NH3). However, the reported photocatalysts suffer from low efficiency with great room to improve regarding the charge carrier utilization and active site engineering. Herein, a porous and chemically bonded heterojunction photocatalyst is developed for efficient PNRR to NH3 production via hybridization of two semiconducting metal-organic frameworks (MOFs), MIL-125-NH2 (MIL=Material Institute Lavoisier) and Co-HHTP (HHTP=2,3,6,7,10,11-hexahydroxytripehenylene). Experimental and theoretical results demonstrate the formation of Ti-O-Co chemical bonds at the interface, which not only serve as atomic pathway for S-scheme charge transfer, but also provide electron-deficient Co centers for improving N2 chemisorption/activation capability and restricting competitive hydrogen evolution. Moreover, the nanoporous structure allows the transportation of reactants to the interfacial active sites at heterojunction, enabling the efficient utilization of charge carriers. Consequently, the rationally designed MOF-based heterojunction exhibits remarkable PNRR performance with an NH3 production rate of 2.1 mmol g-1 h-1, an apparent quantum yield (AQY) value of 16.2 % at 365 nm and a solar-to-chemical conversion (SCC) efficiency of 0.28 %, superior to most reported PNRR photocatalysts. Our work provides new insights into the design principles of high-performance photocatalysts.

Heritability, signal perception and autoregulation of root nodulation in chickpea

Chickpea (Cicer arietinum L.) establishes symbiotic interactions with Mesorhizobium to develop root nodules where nitrogen fixation occurs. This symbiotic relationship can fix atmospheric nitrogen (N2) up to 140 kg N/ha that contribute nearly 80% nitrogen requirement of the crop. Global researchers had revealed the existence of natural variations in chickpea germplasm for nodulation traits with high heritability. Surprisingly, the contribution of environmental variation is too low for Biological Nitrogen Fixation (BNF) traits and high broad-sense heritability (>60) was observed for early nodulation, late nodule senescence and high nodule number traits. Correlation studies indicated a strong positive correlation between nodule number at flowering stage with total nodule weight and plant biomass and seed protein content. Nod Factor receptors in chickpea (CaNFR1 and CaNFR5) are characterized recently that forms phylogenetically distinct group along with M. truncatula, P. sativum, and L. japonicus. Critical role of cytokinin signalling through members of two component system (TCS) in nodulation was investigated in chickpea. The chickpea ortholog CaHK19 was the master spigot of cytokinin perception in chickpea. The co-expression pattern of CaHKs and CaNIN clearly indicated a link between cytokinin perception and downstream expression of CaNIN in chickpea as earlier established in Medicago. Genes involved in AON pathway are partially revealed in chickpea. CaRND1, CaRDN2, and CaRDN3 (C. arietinum Root-Determined Nodulation) function as receptors for signals produced from the roots. Revealing the molecular basis of root nodule organogenesis and their regulatory mechanisms along with identification of potential genetic stock will help on breeding or engineering chickpea genotypes with high symbiotic efficiency, extended nitrogen fixation and high symbiotic efficiency make grain legumes as nitrogen fixing factories to fertilize the soil in a sustainable way.

Promoting the hydrogen spillover via dual active sites synergistically for efficient photo-driven nitrogen fixation

Photocatalytic ammonia synthesis is heralded as the most promising field that will certainly gain increasing attention as a sustainable strategy for low-carbon NH3 production and H2 storage. However, one great challenge is to design ideal catalysts, which can provide the energetic active sites for nitrogen activation and hydrogen dissociation at the same time. In this study, we report that efficient photo-driven ammonia synthesis can be realized by synergetic effect of abundant Mo (V) species and Pt under ambient conditions. More specifically, the optimized Pt-loaded MoO3-x photocatalyst has attained the superior NH3 production rates of 3456 μg·g−1·h−1 under visible light irradiation (≥400 nm). As evidenced experimentally and theoretically, the enhanced photocatalytic performance can be ascribed to dual-active sites, where the loaded Pt co-catalyst can boost hydrogen spillover from Pt to MoO3-x induced by OV due to the low barrier of H* migration between hydrogen activation sites (Pt-O bridge) and nitrogen activation sites (low-valence Mo species), further increasing the number of Mo (V) active sites. And Mo (V) species adjacent oxygen vacancy with outstanding electron-donating capability and strong nitrogen chemisorption played a crucial role in facilitating nitrogen dissociation. Therefore, synergizing abundant Mo (V) species and loaded-Pt can optimize the photo-driven nitrogen reduction and hydrogen oxidation. This work provides a new idea for the rational design of efficient photo-driven ammonia synthesis.

Assessment of legume species for biological nitrogen fixation potential in smallholder farming systems of Kiambu County, Kenya: A participatory approach

This study examined the Biological Nitrogen Fixation (BNF) potential of various legume species in Limuru, Kiambu County, Kenya, focusing on smallholder mixed crop-livestock farmers. Nitrogen is vital to plant growth, particularly for protein synthesis and photosynthesis. Biological nitrogen fixation (BNF), a process by which legumes transform atmospheric nitrogen into a usable form, increases soil fertility and decreases synthetic fertilisers need. The problem addressed was identifying the most effective legumes for improving soil fertility in this region. Using purposive sampling, community-based organisations (CBOs) participated in focus group discussions, where farmers planted experimental plots, collected soil samples, and counted nodules. Destructive sampling was employed during flowering to assess nodulation, with nodules classified based on their ability to fix nitrogen. Results showed Rose coco beans ranked highest due to their efficient nitrogen fixation and adaptability to varying soils and temperatures, followed by Albus lupin and Black and White faba beans. Desmodium also demonstrated persistent nodulation, while indigenous Kienyeji legumes, though less efficient, improved soil fertility. Garden peas, cowpeas, and green grams had lower nitrogen-fixing performance in Limuru's cool, humid climate. This study concludes that Rose coco beans and Albus lupins are highly suitable for improving soil fertility in the region. Participatory methods strengthened farmers' knowledge of sustainable agriculture, and qualitative data highlighted the practical value of BNF legumes. Future research should expand legume trials and explore the use of rhizobia inoculants to further enhance BNF efficiency, supporting long-term agricultural sustainability.